This invention relates to an efficient and economical method for removing residual hydraulic fluid from hydraulic systems and to the composition of a flushing fluid for accomplishing such removal. In the past, fire-resistant hydraulic fluids containing polychlorinated biphenyls (PCB's) have been used in hydraulic systems. However, in recent times regulations of the federal Environmental Protection Agency have mandated disposal of such fluids because of the carcinogenic potential of PCB's.
In order to accomplish the removal of PCB-containing hydraulic fluid from hydraulic systems in a thorough manner, a flushing fluid has been added to the systems and circulated. Prior to the present invention, the flushing fluid of choice has been hydraulic fluid not containing any PCB's. However, usage of such fluid for flushing suffers the disadvantages of being relatively expensive and requiring long-term storage of large volumes of PCB-containing material.
Various types of solvents have been used in the past for flushing or cleaning hydraulic systems, but each of these prior art solvents suffers from one or more serious disadvantages making it less than completely suitable for accomplishing the objectives of the present invention. Larson U.S. Pat. No. 4,017,329 discloses a method for flushing hydraulic systems with liquid dichlorodifluoromethane under a pressure of about 70 psi at 70.degree. F. Braband et al. U.S. Pat. No. 3,385,735 claims a method for cleaning hydraulic systems relying upon alternate washings with a cleaning solution containing an alkaline inorganic compound or synthetic detergent and a solution containing an inorganic or organic acid.
Some other patents disclosing flushing fluids or cleaning solutions different from the ones claimed herein are as follows: Katsuragawa et al. U.S. Pat. No. 3,848,004 (liquid 1,1,1-trichloroethane stabilized by addition of 1,4-dioxane, acrylonitrile, ethyl acetate and nitromethane to prevent rusting of aluminum, iron, zinc and copper); Clementson et al. U.S. Pat. No. 4,023,984 (method for cleaning printed circuit boards using a mixture 1,1,1-trichloroethane and isopropanol); Goodner et al. U.S. Pat. No. 4,046,820 (1,1,1-trichloroethane containing trichloroethylene or fluorene as a free radical scavenging agent to prevent rusting of aluminum or other metals); Safranko et al. U.S. Pat. No. 4,194,924 (method for recovering residual low flash point jet fuel from an aircraft fuel tank by flushing with a high flash point hydrocarbon purging liquid).
While the solvents described in the above patents may be effective for dissolving residual fluids in the systems where they are used, none of the solvents known in the prior art has sufficient viscosity to avoid damaging pumps in hydraulic systems.
It is a principal object of the present invention to provide a method for flushing hydraulic systems that avoids damage to the pumps in such systems.
A further objective of the invention is to provide a method for flushing hydraulic systems wherein the volume of resulting waste material flushed from such systems is less than in prior art methods.
It is a related objective of the invention to provide a method for flushing hydraulic systems that prevents excessive wear on metal surfaces of components in such systems.
Another objective of the invention is to provide a flushing fluid that is a solvent for hydraulic fluid, has sufficient viscosity to avoid damaging hydraulic pumps and prevents excessive wear on surfaces of metal components in hydraulic systems.
Additional objects and advantages of the present invention will become apparent to persons skilled in the art from the following specification.